


Threescompany

by Saiyurimai



Category: Undertale (Video Game)
Genre: Explicit Sexual Content, F/M, Multi, Polyamory, Self-Insert
Language: English
Status: In-Progress
Published: 2017-12-13
Updated: 2017-12-16
Packaged: 2019-02-14 03:05:12
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 6
Words: 13,728
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12998487
Author URL: https://archiveofourown.org/users/Saiyurimai/pseuds/Saiyurimai
Summary: Follow Sai through her new adventure of her newfound relationship between two very handsome and interesting monsters, one a photographer, the other a teacher who both work at the community college she goes to.





	1. Sai meets Gaster

**Author's Note:**

> Thank you Bucky for the additional inspiration and for being an enabler! XD

Sai grabbed a cart from the grocery store’s entrance, grocery list in hand and coupons in her purse. She smiled politely at the greeter, it was a nice fall day out and she was in a relatively decent mood as she wandered the aisles. 

She wanted to take her time, there wasn’t anything going on, no place she really had to be. She wandered down the snack aisle, her goal in sight as she looked upon the brightly colored boxes of artificially colored treats looking for something very specific.

Finally, she glanced up the several rows of shelves towards the top most one and she saw the bright yellow of the familiar box of Gushers that called out to her very soul. 

She looked up and down the aisle first before trying to jump for it, her fingers just grazing the box’s side. With a huff she steeled herself again and jumped, determined to get the last box if it was the last thing she did.

Her heart sank as she felt the box tip over, pushed back and now hopelessly out of reach. All she wanted was some of that sugary sweetness, was that too much to ask? 

Sai glared accusingly up at the last little bit of the box she could see over the edge of the shelf. She really didn’t want to just walk away and give the box the satisfaction of living another day. 

But it was too high for her short five foot four inches to reach and she didn’t really feel like climbing the possibly unsteady shelves in case she made a huge mess of things.

“Excuse me.” A deep voice jolted her out of her thoughts, glancing over to see a tall skeleton monster wearing a comfortable looking grey turtleneck sweater and long black pants, a lengthy black trench coat covering his shoulders. 

“Oh! Sorry I didn’t see you there! I’ll move out of your way.” Sai apologized, stepping aside so the tall skeleton who must’ve been at least 6’4” could look over the snack section. 

A little piece of her cried as his long fingers easily grabbed the last box, turning to walk away in defeat when the skeleton handed it to her with a soft smile on his face.

“Here you go. You looked so crestfallen I figured that I’d give you a hand.” Sai took the box and gave a happy little squeal before wrapping her arms around him in an embrace. 

“Oh thank you so much!” She exclaimed, feeling him wrap his arms around her in an embrace, a chuckle rumbling through him as the scent of ink and books wafted around her, the scent making her smile softly. 

“You smell amazing, like a library full of books…” She flinched slightly as she looked up at the skeleton monster, violet eye lights kind and dark.

He winked and grinned seductively, “Well, you can certainly check me out any time.”

Sai stared up at those violet eye lights, her heart swelling as he had responded with one of the absolute cheesiest pick up lines she had ever heard, the words were out of her mouth before she could comprehend that she’d even said them. 

“Marry me…” The skeleton blinked in surprise, tilting his head slightly to the side, giving her enough time to realize that she had just in fact proposed to a total stranger solely on the basis of him handing her a box of Gushers and a pick up line.

Her face slipped into an expression of abject horror as she quickly stepped away from the monster, tossed the yellow box into the cart and bolted down the aisle as fast as her legs could carry her. 

“Wait! Hold on!” She heard the foot steps clicking behind her, his long legs easily catching up to her shorter ones in less time. “You forgot your library card!” He beamed, handing her a small business card with his name on it. 

Dr. W.D. Gaster, Professor at the local University, his phone number quickly and elegantly scrawled on the bottom of it in purple ink. Sai’s face turned beet red as she looked up at the tall skeleton who shrugged.

“Would you like to meet up for coffee sometime? My treat?” He smiled hopefully down at her, towering over her but not in an intimidating way. It took a moment for it to register that he was asking her out as she looked at him and down at the card and then back at him. 

“Yeah. I’d like that.” She grinned, Gaster breathing a soft sigh of relief as he put his hand in one of his pockets, pulling out a grocery list, asking her where some of the items were located in the store. Sai was more than happy to show him around.


	2. Sai meets Grillby

**Summary for the Chapter:**

> Sai is running late to class...

Sai slammed her car door shut, slinging her bag over her shoulder and cursing under her breath. She should've left earlier. She shouldn't have turned off her alarm. Now, she was late to her class at the community college. The same college that Gaster taught at.

 

She weaved through the group of students easily, waving to a couple of people she knew but otherwise focused on trying to make it to class before her teacher would mark her as absent. She'd had coffee the day before with Gaster, the skeleton monster was a very handsome and very interesting character. Sai had even made plans to go back out with him for coffee again sometime soon.

 

Her mind was elsewhere as she started to walk through the courtyard, pulling out her phone to check the time again. She was going to get there probably as soon as the teacher did. She wondered what it would be like to take one of Gaster's classes. Was he a good teacher? He seemed really smart by the way he talked and the way he acted.

 

She was so focused on her own thoughts that she didn't see the group of students posing in the courtyard. She didn't even see the professional looking photography equipment. Nor did she see the flame monster kneeling on the ground until it was too late.

 

"Ack!" She cried out as they both went sprawling to the ground. "What the-?" Came a deep voice from under her as she found herself straddling the tall flame elemental, her gold eyes meeting his white ones. "I am so sorry! I wasn't paying attention to where I was going I am so sorry!" Sai apologized her face turning bright red as she looked down at him under her.

 

"That's alright. I'll take this shot any day." He chuckled and her flush deepened as she realized just what kind of position they were in. "Oh my god. i am so sorry." Sai stuttered as she got off of him, standing up and watching him get off the ground, dusting himself off, a camera hanging around his neck. "No harm no foul. I'm Grillby. What's your name?" He asked, looking over his camera, pulling a cloth from his breast pocket and cleaning the lens.

  
"Sai. I'm sorry I ruined your shot." She brushed her hair behind her ear, glancing over at the small group of students who had stopped posing while the two of them talked. Then she heard the click of the camera and turned to look at him in surprise. "No worries, got a better one." He looked at the screen of the camera with a soft smile on his face, making her blush. "Nice. Much better than the other ones I've taken." He winked up at her and she found herself at a loss for words. What was she supposed to say? "Thank you...?" She responded softly as he stepped towards her, reaching into one of his pockets for a card with his name on it.

 

"Call me sometime. I'd love to take more pictures of you for the school website. The camera loves you." She took the card with a bright red flush to her cheeks. Holy crap. Not one but two numbers in the same month. "Sure, sounds good." She nodded, staring up at him for a moment before feeling her alarm go off on her phone. "Shit! I'm so late for class! Sorry! I've gotta go!" She jumped, brushing past him and running towards her class, not seeing the way Grillby watched after her with a smirk on his face.


	3. Sai gets a date

**Summary for the Chapter:**

> Sai finds herself in an unusual situation...

Sai was sitting in her apartment, finishing up some homework when she took a glance at her clock. Shit. Was it that late already? Rubbing her face she put her books down and hopped off the bed, stretching and stifling a yawn. She walked to the kitchen, thinking about making something for dinner but deciding against it as she grabbed her keys and a coat, slipping on her shoes and getting into her car.

 

It was too late to make something. Besides, she would have to do all the dishes afterwards and she just did not want to. Sai drove a little ways away to a restauarant she liked to go to when she didn't want to cook, it was cheap enough that it wouldn't kill her pocket book and the food was good enough that she never left hungry. Plus the service was always nice and she was sort of a regular there now. Sai pulled into the parking lot, the place wasn't usually busy this time of night which was nice and meant the food would come out faster than normal.

 

With a happy little hum Sai walked into the building, greeting the hostess with a smile. "Just can't stay away huh Sai?" The hostess smiled, grabbing a menu as Sai shrugged with a grin. "What can I say, you guys are delicious." She started to follow the hostess to a table when she heard her name being called, causing her to pause as the voice sounded familiar. When she turned she could see Gaster taking off his long coat at another table, putting it over the back of a chair. "Sai. It's a pleasure to see you again." He smiled as he came over to them, the hostess setting her menu down and going to grab a glass of water for her.

 

"Are you here with anyone?" He asked, looking around with his violet eye lights as she tried to hide the flush on her face. He was so tall, and holy hell was he attractive. "Uhm no. It's just me tonight. I didn't feel like cooking so I sometimes come here to grab a bite." Gaster returned his gaze to her, a pleasant smile on his face as he gestured to his table. "Would you care to join me then? I would enjoy your company." Sai looked at the table, seeing two menus and two glasses of water sitting there. He was clearly waiting for someone to join him and she was hesitant to intrude.

 

"Oh no I don't to intrude on you and your friend! No worries." She smiled, raising her hands but he only tilted his head and gave a soft chuckle. "Nonsense. They're running late anyways and I'm sure they would be more than happy to meet you Sai. Please. I insist." She thought for a moment, well if he insisted. She finally nodded and allowed him to guide her to the table, his hand grazing the small of her back as he pulled out the chair for her, ever the gentleman.

 

"Thank you. Are you sure that they won't mind? I don't want to cause any trouble." She asked as he took a seat on her right and he took a sip of water shaking his head. "No. It's no trouble at all. Honest. Besides I thoroughly enjoy your company and I'm sure they will as well. How have you been? Are you excited for the winter break?" Sai relaxed easily into the conversation with him. He was always so intent on whatever she had to say and he was easy to talk to. He threw a couple of jokes her way which made her laugh, even though they were terrible. She loved bad jokes and puns, and the cheesier the pick up lines the better.

 

They ordered their food, Gaster ordering for his guest who had sent him a text saying they were on their way. Gaster leaned forward towards her as they waited for the food to arrive. "I have a personal question if you don't mind." Sai blinked in surprise, unsure as to where exactly it was going but curious nonetheless. "Are you single? I mean are you seeing anyone currently?" He asked, a twitch of a smile on his face as she blushed. Oh. Oh! He was interested! Well, obviously he must've been at least a little interested since he'd given her his number and they'd had coffee together a couple of times. "I'm not seeing anyone. I've been single for almost two years now, just been really focusing on classes and getting my life together you know? But now everything is going really well so I've been thinking about getting back out there again." Sai tried to hide the blush that came to her cheeks as Gaster grinned with satisfaction.

 

"I see. That's good." He mused as the food arrived, at the same time a familiar flame elemental came up behind him. "Sorry I'm late. I was trying to edit some photographs I took the other day and lost track of time." Grillby leaned down and gave Gaster a kiss, the skeleton leaning into him slightly with a smile on his 'lips'. Sai felt her heart sink a little bit at the sight. Of course. He was just being polite, making conversation.

 

Grillby took a seat, shrugging off his jacket and running a hand through the softly crackling flames that served as his hair, doing a double take at her as he realized who had joined them. "Sai? Didn't think I'd be seeing you again so soon." He smirked to her left, leaning back in his seat as she took a drink of her water to avoid answering right away. Gaster looked between them in surprise. "You two know one another? What a coincidence. This is the woman I was talking to you about, the one from the grocery store." Grillby tilted his head slightly, raising a brow at her as she tried not to squirm in her seat. They talked about her? Of course they would, they were together. That's what couples did. They were a couple. An incredibly attractive couple.

 

"The one with the Gusher addiction. And the new face who will be featured on the front of the school website." Grillby took a bite of his food, nearly making Sai choke on her own food at his announcement. She swallowed and took a hasty sip of water that made both of them look at her in amusement. "Excuse me what?" Sai finally managed and Grillby chuckled pulling out his phone, typing something in and handing it to her. She looked down and saw the school's web page pulled up and there she was. Right on the front page. "The camera loves you. I must say it is one of my favorite ones I've taken so far." Sai handed the phone back and he handed it to Gaster so he could see for himself.

 

"Wow, I really like this one. It looks so natural and the lighting works really well together." Sai swallowed nervously. So Grillby was also just being nice too. He just thought she looked pretty enough for photos. Neither of them were romantically interested in her. That was fine. No big deal. She didn't really expect them to be but it was a nice thought nonetheless while it lasted. She listened to them talk a moment, eating quietly as they talked about their days to one another. She was just a third wheel.

 

"I think that's a grand idea. What do you think Sai?" She blinked, staring blankly as she heard her name. She'd droned out, not wanting to invade their conversation and hadn't heard a word they'd said. Now both of them were looking at her and she had no idea what to say. "You weren't listening were you?" Grillby eyed her with a knowing smirk, scooting his chair closer to her so that their knees touched under the table. "Don't scare the poor girl Grillby." Gaster's hand lay atop hers on the table comfortingly and her heart raced inside her chest as Grillby leaned in closer to her.

 

"Aw, you aren't scared of me are you Sai? I mean," He was so close, his warm breath rushed over her cheeks and she couldn't look away from him, "you wouldn't agree to go out on a date with someone who scared you would you? So what do you say little one? We can show you a good time." Grillby eyed her over his glasses, oozing with confidence, domination that spoke to her more submissive tendencies as she swallowed reflexively. "Say yes." He breathed when she hesitated and before she realized it she was saying, "Yes." He chuckled and pulled away, allowing her to blink, realizing that Gaster had intertwined his fingers with hers.

 

"You're always so forward." Gaster admonished as Grillby leaned back in his chair with a shrug. "I got an answer and a very good read on her personality." Gaster gave a chuckle and Sai tried to figure out what the hell just happened. "Sai? Are you alright with this?" Gaster asked, grabbing her attention with the soft question. "I-I'm mostly just a..." She couldn't find the words as she looked between the two of them, Grillby leaning back in his chair with his arms crossed over his chest, eyeing her like she was some sort of prey. The thought of it sent a strange shiver down her spine.

 

"Confused? I imagine you are. So let me clarify if I can for you. We are looking for a third to join our relationship. We are polyamorous and you seem like a good fit for us." Gaster explained with a smile, looking a little cautious of her reaction. Sai had heard of that sort of relationship although she'd never been in one herself. It was a curious thing but not an altogether deal breaker for her. "We'll explain more once you decide if this is something you would be interested in joining. But I'm afraid I have a class to teach in the morning and we must get going here soon." Grillby grabbed the check off the edge of the table. When had the waitress brought it? Had she just spaced out this entire time?

 

"We'll pick you up at seven thirty sharp this Saturday. Dress nicely." Grillby stood, both of them putting on their jackets as the flame elemental bent down next to her ear, "And don't leave me waiting." He winked as he walked to the front to pay the bill, Gaster shaking his head. "Seems he's really taken a shine to you. I knew he would and I'm glad you agreed to go out with us. We will see you Saturday Sai. Have a good night." Gaster smiled, following Grillby who held open the door for him, giving her one last glance as she sat at the table. She didn't move for a few moments as she tried to process what had just happened.

 

The waitress came over and asked if she was alright and she nodded politely, gathering her things and taking one last drink of her water before getting into her car and heading back to her apartment for the night. There was no way she was going to be able to study after this.


	4. Sai's Date Night

**Summary for the Chapter:**

> Sai is nervous about her unconventional date...

Sai rummaged through her closet, standing there contemplating what she should wear. Grillby had said for her to dress nicely but how nicely did he mean? The two of them seemed to dress so smartly all the time, she just wanted to be able to look like she belonged with the two of them. She had her hair pulled up in the towel as she pulled out three of her nicest outfits.

She could wear black? She'd only ever seen Gaster in varying shades of it and it was a very flattering color. But she also kind of got the idea that it would send the wrong message. Whatever that message was. She put it back and ultimately put back the red one too for the same reasons. Too flashy. She didn't want to stand out like a sore thumb. Sai decided on the navy blue off the shoulder dress. It was flattering to her figure as she zipped it up in the back, the skirt portion flaring out slightly just above her knees, an intricate lace design covering it that she really liked. Plus, she thought, it complimented her eyes really well.

  
She sat down at her vanity and went about putting on a natural look of makeup, her eyeliner coming to a sharp point, red lipstick making her lips pop against the blue. She had left her curling iron on to heat up and when it was done she went about curling the ends of her purple hair, the red tips standing out. She pulled some of it up into a little ponytail, pinning a matching navy blue bow to it to keep it in place, the majority of her hair trailing down to the middle of her back in soft curls. She put on a simple gold necklace before putting on the navy and gold pumps that she'd bought with the dress. She took a moment to look at herself in the full length mirror, making sure everything looked alright.

 

"Mom always said I cleaned up nice." Sai said to herself with a soft smile at her lips. Taking a quick glance at her clock she took a steady breath as 7:30 came ever closer. She grabbed her nicest coat and put it on, grabbing her phone and purse just as she heard knocking on her front door, making her squeak softly in surprise. "Coming!" She called out as she did one final check and opening the door to see Gaster and Grillby standing there waiting for her. "Right on time." Grillby smirked, eyeing her appreciatively as Gaster muttered something under his breath that she couldn't hear.

 

"We got you some flowers." He finally managed, handing her a bouquet of pretty wildflowers which made her blush a little in surprise. "Wow, thank you. Let me put these in some water really quick. Would you...like to come in for a minute?" She stepped aside, letting them walk into her modest apartment. "Thank you." She closed the door behind them and went into the kitchen while they looked around the living room and she searched for a vase to put the flowers in. She could see them looking around, Gaster moving to her bookshelf, Grillby going to her movie and music collection. Man were they tall, even in her heels she had to look up at them as she grabbed her stool in order to grab the vase above the fridge.

 

"You have a nice place Sai. Your book collection is interesting." She flinched a little as she turned on the faucet. She had a lot of fantasy books, books about magic and dragons, some about fallen angels, many of them involving some sort of love theme. "Thank you." She finally managed as she put the flowers in and brought them out to her coffee table, arranging them nicely and unable to help the little smile that came to her lips. "It's a nice sized apartment and you're on the first floor too. One bedroom?" Grillby asked, glancing over at her from the corner of his eyes as he looked at a piece of artwork she'd done.

 

"Yeah, I really lucked out. The rent is nice too." Sai wrung her hands together a little nervously as the two of them turned their gazes on her. Grillby came closer to her, grabbing her chin in his fingers and lifting her face to look up at him. "You clean up real nice. I like the bow." He smirked and it sent her heart racing. "T-thank you." She responded in a soft whisper as Gaster came up beside her, fingers splayed over her lower back lightly, moving to wrap around her hip, pulling her against his side.

"Are we ready to go? I don't want to miss our reservation. Plus it'd be a shame to not show off Sai here to the public since she looks so nice." Gaster smiled down at her as Grillby straightened, a gleam in his eye as he nodded. "It would be. Let's go." Grillby walked towards the front door, Gaster and Sai following suit behind him, Sai pausing to lock up her apartment before following them out to the parking lot and towards a black midsized SUV that looked like it'd just come off the assembly line.

 

Gaster opened the back door for her, thanking him as she climbed into the back of the vehicle. Grillby got into the driver's seat, Gaster sitting next to him upfront while she sat in the middle so she could see where they were taking her tonight. "So, how long have you two been together?" She asked a little awkwardly as Grillby put the car into drive and pulled out of the parking lot. "About four years now. Although we've known one another for a lot longer than that." Gaster glanced over at her from the front seat, a smile on his face. Sai nodded as she cleared her throat. This was a little awkward. She sort of felt like a child sitting in the back seat by herself. She also had no idea what else to say to them. This was a whole bunch of firsts for her.

 

"How many...I mean...is this something you guys...You know...do a lot?" She asked and Grillby chuckled, glancing at her in the rearview mirror. "If you're asking if you're the first then yes and no. You're the first woman we've wanted to bring into our relationship but not the first person we've been involved with." Gaster explained, turning a little more towards her as Grillby navigated the streets towards the nicer part of town. She blushed a little bit, tucking a strand of hair behind her ear.

 

"How does that even work though? Do you guys ever get jealous of one another? How does this sort of relationship work?" She asked, nervously trying to fill the silence. Gaster smiled calmly at her while Grillby chuckled in the driver's seat. "We divvy up the time equally, set up boundaries, such as no dating outside of the relationship, no sleeping with anyone else, making sure that none of us are left out. It's really just the same as a regular relationship, with an extra person. If someone does get jealous it's important to make it known and resolve the problem quickly. If it can't be resolved or there are other issues that are in the relationship then there's no point in continuing the relationship with them." Gaster explained, putting her a little bit at ease with his calming tone.

 

Grillby turned into a parking space and parked the car, getting out and opening the door for her as Gaster got out. He held out his hand for her and she took it, stepping out of the car, his hand moving to wrap around her waist, guiding her towards the front of the restaurant, Gaster placing a hand on her upper back, sandwiching her between them as they entered, walking up to the host stand. "Reservation under Grillby for three." The flame elemental taking the lead as Gaster pulled her slightly to his side.

 

The host smiled politely but Sai had a weird feeling that they were judging her right now as they walked towards the back of the restaurant to a large booth that seemed relatively private. Grillby slid in first, patting the seat next to him. "Come. Sit." Gaster took off her coat for her, taking it and their coats and handing it to the host who hurried to put them out of the way for them. Sai swallowed nervously, looking to Gaster for a moment as he motioned for her to move in next to Grillby. She slid in next to Grillby who put his arm on the back of the booth behind her, Gaster moving to her other side.

 

The server came up and greeted them, Grillby taking the lead once again and ordering an appetizer, some expensive sounding wine, the server nodding happily and going off to put in the order, giving them a moment to look through the menu. Sai opened hers and balked at the prices. "Order whatever you'd like Sai. Don't even look at the prices." Grillby leaned in a little bit, noticing her uneasiness. She looked through and saw that there was some relatively reasonably priced pasta dishes. "What are you thinking of having tonight hm?" Gaster leaned over her slightly, so close.

 

"Uhm...this chicken alfredo sounds good. Is that alright to order?" She asked and Gaster gave her an approving smile. "Of course it is." Just then the server returned with their drinks and the appetizer, asking if they were ready to order. Grillby and Gaster ordered for her and then themselves, handing the menus back to the server who left them alone again. Grillby turned more towards Sai, Gaster mimicking his position on her other side. "Gaster tells me that you've been single for quite some time. Why is that?" Grillby asked and Sai shrugged.

 

"Just, haven't really found the right person I guess. It wasn't like my last relationship was awful it just wasn't what I wanted at the time." Sai explained, taking a sip of her glass of wine, blinking in surprise at the taste. It was good. Really good. She didn't even want to know how much a glass of this actually cost. "Hm. Interesting." Grillby took a sip of his wine, Gaster grabbing one of the appetizers and holding it out for her. "Open." Sai did so, Gaster popping the food into her mouth, her lips brushing against his finger briefly as she chewed.

 

Gaster took another piece, eating it himself, eye lights glancing over at her for a moment. "Good right? I love this stuff." He said when he was done chewing, Sai nodding with a small smile. She was still nervous but the good wine and the food was starting to settle her down a little more. Grillby's leg kept brushing against hers under the table, warm, a passing thought making it from her brain to her mouth without realizing it.

 

"How come your clothes don't just burn off of you?" She asked curiously, taking a sip of wine, Grillby chuckling and looking down at her, the soft crackling of his flames seeming to spark as he leaned in closer. Sai blushed deeply at how close he was, his hand grabbing hers and placing it against his exposed neck. Sai was almost convinced that direct touch would burn her so when she was met with something solid underneath the tickling flames she was almost fascinated. "You know, if you wanted to see me naked all you have to do is ask." He breathed, a tongue of flame licking her parted lips teasingly.

 

Sai didn't get a chance to respond more than a surprised gasp as their server returned, Grillby moving back to his original position while the food was put on the table. The server asked if they could refill their glasses, "Just leave the bottle. Thank you." Gaster smiled politely while Sai put her napkin in her lap, the smell of the pasta making her stomach rumble hungrily. The bottle was brought out and Gaster thanked the server again, taking it and her glass, refilling it along with the other glasses on the table. 

 

"This looks so good!" Sai, momentarily distracted from her nervousness and from the pounding of her heart didn't see the look that passed over her head between the two monsters. Sai took a bite, and practically melted. Oh, oh man was that good. Probably the best thing she'd ever tasted. She took another couple of bites and giving a soft happy moan and a little wiggle. She'd almost completely forgotten that she was there with other people until she heard a couple of chuckles on either side of her.

 

"That must be some pasta, may I?" Gaster asked, and she nodded with a smile, the food was enough for her to feel better about being there with them. Gaster took a bite, deep purple tongue licking his lips clean of the white sauce with a smile. "Why don't you give some to Grillby? He should try it too." Gaster nodded towards Grillby who was looking at her again. Sai used her fork, twirling the noodles onto the fork neatly, and holding it out for him. The flame monster kept his gaze locked on her as he took a bite, chewing slowly, a little bit of sauce at the corner of his mouth.

 

"You uh...you have a little bit...right there." She pointed to the corner of his mouth only to have him lean forward towards her again. "Oh? Well, we don't want it to go to waste do we?" Sai had a feeling that he wanted her to lick it off but even though she was extremely tempted to do it she was hesitant. After all, she wasn't exactly sure about the dynamic between the two of them. "Go ahead sweetheart." Gaster purred from behind her, his face at her ear, a hand resting on her hip encouragingly.

 

Sai swallowed and leaned forward, using the tip of my tongue to lick the bit of sauce from his mouth, Grillby smirking as he captured her mouth in a kiss. Sai gasped in surprise, allowing Grillby to deepen the kiss, one of his hands moving to cup her cheek while Gaster placed a tender kiss on her shoulder, sending a chill down her spine, delightful and full of energy. This was...This was very nice. She could only imagine what it might feel like if...Grillby broke the kiss, bringing her back from her thoughts as he winked at her, going back to his meal.

 

Gaster gave a final kiss against her skin before doing the same, leaving her flushed, heart racing as she returned to her meal, flicking glances over at the both of them in between bites. Oh boy what had she gotten herself into. The rest of the meal was relatively quiet, filled with feather light touches that left goose bumps on her skin. She could tell that seeing her flustered was entertaining for them, occasionally catching either of their gazes. They would ask her questions about herself, mostly harmless like what she was studying, how long had she been in school, what her favorite color was, that sort of thing.

 

Sai answered them, usually earning a pleased smile or even another one of those feathery touches. It seemed that her drink was always full, Gaster or Grillby making sure to keep it filled. She was a little tipsy, her cheeks a little flushed but she wasn't entirely sure it was because of the wine. Having both of their attention on her, it was...nearly overwhelming. By the end of the meal she was full, a little tipsy and unintentionally leaning up against Gaster who had an arm around her waist, fingers intertwined with hers.

 

"I think someone might be ready for bed." Gaster smiled and Sai watched as Grillby put a card in the black check book, setting it on the edge of the table. "Or we're boring her." Sai shook her head a smile on her face. "No! Of course not! I'm having a great time actually. I'm just full and I've been up since early this morning. I swear I'm good." She smiled at Grillby, hearing a soft chuckle from Gaster. "I think I've made my decision and I know Gaster has already." Grillby shared a look with Gaster who nodded as she sat up straighter.

 

"What decision?" She asked, glancing between them, not entirely sure what they were talking about. "Would you like to continue to see us? Romantically of course." Gaster turned her face to him with one of his long fingers on her chin. She hadn't thought she would ever be interested in something like this. To be involved with both of them at the same time, was something she wasn't used to. But she really did like them. Grillby a smoldering dominant force, Gaster more calming but still there was something magnetic about him that she found intriguing.

 

"Say yes..." Grillby breathed at her ear, nipping at her lobe teasingly, a soft sound escaping her lips. "Yes." She breathed, Gaster's mouth curling into a grin as he closed the distance between them in a slow languid kiss. Grillby brushed her hair aside, planting a kiss between her shoulder blades as she leaned into Gaster's kiss, his hands running down her sides pleasantly.

 

Sai tried to collect her thoughts as Gaster broke the kiss, leaning over her slightly to kiss Grillby, hands on her thighs and her lower back, somehow still making her feel included as they kissed. Finally they pulled away from one another, a deep blush on her cheeks as they looked down at her in unison. Grillby took his card back and the paid check, putting them back in his wallet as he got up, holding out his hand for her which she took, Gaster following behind them, both of their arms wrapped around her back. Sai noticing the stares they were getting from the other people, Gaster glancing down at her as she seemed to shrink a little.

 

"Ignore them. They're only jealous that we get to have you all to ourselves." A flush crossed her cheeks as Gaster helped her into her coat. "Exactly. Now let's get you home." Grillby handed Gaster the keys and walked back out to the car. Grillby climbed into the backseat with her, bringing her close to him in a deep kiss. Gaster started the car and pulled out of the parking lot as she found herself being pulled under him on the back seat. She gasped into the kiss as she felt his hand run under her dress, the flames brushing against her skin as he kissed down her throat.

 

Sai was in a haze as she arched into his touch, he didn't do anything more than kiss and touch her and yet...had it really been that long since she'd been touched like this? It'd been too long...she thought as a soft moan escaped her lips when he nipped at her collar bone. "We're here." Gaster said all too soon and she unknowingly gave a little whine as Grillby pulled away from her. "Aw. Don't worry babe. You'll see us again real soon." He winked as he gave her one more kiss, allowing Gaster to help her out of the car and walking her up to her apartment.

 

"You'll have to wait only a little longer. We don't go all the way on the first date. Besides you've been drinking and we would rather have you fully in control of yourself before we push any further." Gaster pulled her into an embrace, kissing her deeply, taking her breath away as her hands rested on his chest, standing on her tip toes. "Good night Sai." He breathed, kissing her softly again before stepping away for her to open her door, smiling as he turned and left to join Grillby in the car. Sai watched them go, heart racing in her chest and her body flushed and left wanting. Oh this was going to be interesting...

 


	5. Sai makes dinner

**Summary for the Chapter:**

> Sai invites the guys over for a home cooked meal...

Sai double checked her phone, seeing the text message from Grillby saying they were on their way to her place, a smile crossing her lips as she saw the little winking face he always seemed to put at the end of his messages to her. She'd been dating Grillby and Gaster for a couple of weeks now, almost a month and to be honest she was enjoying it quite a bit.

 

She'd started to get a real feel for their personalities now. Grillby was definitely the alpha male in the relationship, all dominance and really handsy no matter where they were at. It was a source of amusement to see her all flustered, all worked up and then leaving her wanting more. Gaster was a more subtle type of passion, he was relatively quiet, tender touches and longing kisses that would take her breath away. Although she could tell that he too had a tendency to be amused whenever she would get worked up, always giving her one more touch, one more kiss to help tie her over to the next time they would meet.

 

She pulled her hair up away from her face into a high ponytail, pulling out the ingredients for the meal she was going to cook for them. She soon got busy with all the prep work, glancing between the recipe and the food to make sure she was doing it right. Sai was so engrossed in what she was doing that she almost didn't hear the knock on the front door.

 

"Come in! Door's open!" She called over her shoulder, hands covered in chicken that she was busy butterflying. She smiled as a pair of arms wrapped around her waist, Gaster kissing her cheek in greeting. "Hello." He spoke softly, resting his chin on her shoulder for a moment, Sai leaning into him in return. "Hey, I hope you guys are hungry." Gaster kissed her cheek again, letting her go, fingers lingering on her as he moved to the living room, putting his coat on the new hooks she'd placed on the wall specifically for them.

 

"Nice breasts, what are you making?" Grillby tugged playfully on her ponytail and she turned to look at him with a soft giggle. "Chicken cordon bleu." She answered as he kissed her on the lips, hand snaking down to give her rear a tap which made her gasp in surprise, Grillby chuckling as he pulled back from her, handing Gaster his coat and leaning up against the counter with his arms crossed over his chest.

 

"How did you do on your finals Sai? Did those note cards help you any?" Gaster asked from the other side of the counter, taking a grape from a bowl sitting out and eating it. Sai nodded, going back to the food preparation, glancing up at him through her lashes. "Yeah, they really did. Thank you by the way. I think I may have passed my finals with at the very least a solid B." She smiled, glancing at the recipe for a moment and turning towards the fridge to grab the stuff to go inside of the chicken, smirking as she bent over, taking her time in finding what she needed.

 

She'd decided on a pair of skin tight black leggings and a nice low cut shirt for the night, hoping to possibly give the guys a taste of their own medicine. Finally she grabbed what she needed and stood back up to see the two of them watching her, gazes amused but following her as she went back to making dinner. "How will your grades be then do you think?" Gaster asked, he was certainly the one who seemed more concerned with her studies, it must be the teacher in him she thought. "It won't move it too much, I'll still have an A, keeping with my track record. So don't worry about it." She heard the chuckles and smiled to herself.

 

"Do you need any help?" Grillby asked, moving aside so she could get to some of her spices that he was blocking and she shook her head looking up at him. "No thank you. I think I've got it. You two can go pick something to watch on Netflix though and I'll let you know when dinner is ready. Oh! And I've got drinks in the fridge if you want them." Grillby leaned in and kissed her again, running his hand over her ass as he went past her to grab the drinks for him and Gaster. "Let us know if you need our help." Gaster winked, Grillby pulling him in for a kiss before the both of them went and sat on the couch, making themselves comfortable.

 

Sai watched them for a moment, smiling as Grillby allowed Gaster to lean against him, arm over the back of the couch as they talked among themselves trying to decide on something to watch as they scrolled through the Netflix. They were so handsome, she thought as she looked at them. So comfortable with one another and she hoped that someday she would get to that level with them. She was still unsure of herself around them, not wanting to step on any toes with them if she could help it. So far though, everything was going well.

 

Sai finished up the chicken, tying each breast to keep the stuffing inside and placing them in the baking dish, putting it in the oven to cook. She went to wash her hands and the cutting board, not paying attention as she reached for the sprayer, gasping sharply as the water hit her skin suddenly. "Shoot." She cursed quietly under her breath as she went to grab a dish towel to dry off. Seeing both Gaster and Grillby watching her every move and she took a little bit of pleasure as she dabbed at her damp cleavage, pulling the front of her shirt down just enough to show the tops of her bra, giving them a peak of her skin.

 

She smirked as she turned away from them, going to grab her own drink. Licking her lips before taking a drink and getting to work on the other parts of the dinner. She was enjoying having their eyes on her as she worked, making sure to make every movement deliberate, accentuating her figure as best she knew how. A sway of the hips there, a little bit more cleavage here. She glanced up to meet their gazes, violet and white staring at her, Grillby looking hungry, Gaster leaning forward entranced. "What do you think you're doing?" Grillby asked and she feigned innocence, dipping her finger in the sauce for a taste test, licking it slowly. "I'm cooking. What do you think I'm doing?" She popped her finger into her mouth, sucking slightly and giving a soft appreciative moan at the taste.

 

"Sure you are." Grillby smirked, Gaster gave a soft chuckle as she licked her lips clean again. Uh oh...she saw the spark of something dark and primal flash across their eyes. A flush came to her cheeks and she heard the timer go off on the oven. Quickly, Sai busied herself with finishing up dinner, checking the temperature of the chicken to make sure it was cooked through properly, taking it out and putting it on top of the stove, turning everything off and reaching up into the cabinet, not quite able to reach the plates.

 

Why did she insist on putting them up so high? Why was she cursed with being short? She was about to grab the stool when Gaster walked into the kitchen, reaching up to grab them for her. "You really are short aren't you?" He teased and she stuck out her tongue at him playfully, taking the plates from him and hearing the chuckle from behind her. Sai plated up the food, making sure to cut off the cooking twine around the chicken and put the dirty dishes in the sink for later, using her skills she managed to grab all three plates and put them on the dining table which was already set for the night.

 

"Dinner's ready." She smiled over at Grillby who got off the couch coming to stand in front of her, grabbing her chin and leaning down over her. "Be sure to save room for dessert." He winked, kissing her deeply, just long enough to bring her to a fluster before stepping away and taking a seat at the head of the table, Gaster sitting across from her. "It smells delicious." Gaster smiled up at her and she let her hair down. "Thank you. I hope you guys like it. I've only made it a couple times before but I wanted to make something nice for you two." She waited patiently as they each took a bite, anxious to know how they liked it.

 

"Mmm! Very good Sai." Gaster praised and she beamed, glancing over at Grillby as she prepared to take a bite. He took a second bite and wiped his mouth before he took a drink. She knew he was toying with her, it was one of the things he enjoyed and she just waited patiently until he said something. "Grillby...Don't be rude." Gaster noticed and gave Grillby a look. "It's very flavorful. Good job, very good." She took a bite finally, surprising herself with how good it was. It could use a little more pepper though but it was good.

 

They ate together, making small conversation, Sai asking about their days and Grillby talking about getting some new equipment for his little studio. It was...comfortable, she thought. Finally, they'd finished eating and she got up to clear the plates, Gaster helping her while Grillby cleared the rest of the table. "I'll dry and put away if you wash?" Gaster offered as she started washing the dishes, Gaster leaning up against the counter with a towel while Grillby stood behind her leaning up against the wall.

 

Sai was busy cleaning the dishes, not seeing the silent conversation between the two monsters behind her. She was handing Gaster a plate when she felt Grillby's familiar warmth at her back, his hands running down her sides, pulling her hips towards him. "Keep washing the dishes." He kissed the side of her neck, sending a chill down her spine as she felt his hand move over her hip to the space between her legs, fingers brushing against her as she gave a soft gasp of surprise.

 

Sai nearly dropped the plate in her hand back into the water as she felt him rub up against her, his long fingers rubbing her over the leggings. "Keep going, the faster you finish the faster we can take care of you." Gaster leaned over and kissed her cheek, kissing Grillby next to her. W-were they serious? Sai tried to focus as Grillby's fingers probed against her entrance tantalizingly. Did they mean what she thought they meant? Because if it did...oh! Sai moaned, bucking against Grillby's hand as he pressed against her clit through the fabric.

 

She could hear his deep chuckle at her ear, "Faster sweetheart, I'm getting impatient." She licked her lips, finishing up the last bits of silverware, turning off the sink and turned around to face Grillby with a flushed look on her face. "Good girl. Now, both of you. Bedroom." She nodded obediently, Grillby stepping aside for her, slapping her ass sharply, making her yelp in surprise, glancing over her shoulder at him before Gaster guided her back to her bedroom.

 

Gaster and Sai paused at the bottom of her bed, turning to see Grillby closing the door behind them taking a seat in her lounge chair. "Now undress one another. Slowly." Sai blushed beet red, feeling self conscious all of a sudden as she looked between Gaster and Grillby a little nervously. Gaster seemed to notice her hesitation and brought her face to his with a gentle touch, kissing her in that tender way he had.

 

She leaned into his touch, his hands roaming lightly over her body, fingertips brushing against her skin as they moved under shirt, splaying against her stomach. "Arms up little one." Gaster breathed against her lips, taking her shirt and pulling it up over her head, letting the fabric fall to the floor as he kissed down her throat, long fingers trailing over her back as she wrapped her arms around his shoulders, a soft moan escaping her lips. Gaster towered over her, taking one of her hands and bringing it to the top button of his shirt. "That's it." He smiled encouragingly as she started to unbutton his shirt with slightly shaking hands.

 

His fingers brushed aside a strand of hair as little by little his chest was exposed, Sai was interested in the strange deep violet ecto flesh that covered his bones, mimicking muscles and skin. He shrugged off the shirt, taking her hand and placing it atop his chest. "You can touch it. It's just like your skin, just made of magic." He smiled down at her as her fingers traced the outlines of his lean muscles, feeling tiny pulses of sparks against her fingertips. After a moment Gaster kissed her again, pulling her into him as he lay he onto the bed under him, thumbs hooking the hem of her leggings. Sai lifted her hips slightly so that he could pull them off of her, not breaking the kiss.

 

She heard her clothes hit the floor at the bottom of the bed, feeling exposed as Gaster sat her back up, moving her hands to the front of his pants. Sai looked up at Gaster as he cupped her cheek, her fingers undoing the front of his slacks and pulling them down, Gaster's shaft springing free in front of her face. "Go ahead." Grillby's voice came from the side of the bed, his clothes neatly draped over the side of the chair, a deep flush on her face as she saw both of them in front of her in all their glory.

 

Grillby sat behind her, his fingers making quick work of the clasps of her bra, sliding the straps down over her shoulders. He kissed her shoulder blades, one hand cupping her breast, the other sliding between her thighs, making her gasp as one of his fingers slipped between her folds. Gaster took the opportunity of her parted lips, pressing the tip of his impressive deep violet shaft against her mouth, Sai taking the hint and taking it into her mouth slowly.

 

"That's a good girl." Grillby praised as he began pumping his finger inside of her, in time to her mouth on Gaster who groaned, his hand going to her hair. Sai moaned as she felt another finger enter her, Grillby's palm rubbing against her clit, kissing her skin while his fingers rolled her nipple, pinching it lightly, making her gasp, arching her back and taking Gaster a little deeper into her throat.

 

Gaster groaned as she licked the underside of his cock, rolling her hips into Grillby's hand, a moan vibrating through her lips. Gaster's grip tightened on her hair as he started to thrust slowly into her mouth, holding her head still. "That's so good Sai..." Gaster praised as she looked up at him, a soft whine as Grillby removed his fingers from inside of her, earning a chuckle and a kiss to her shoulder. "Don't worry I'm not done with you yet." He grabbed some of her hair, pulling her off of Gaster with a soft pop, a line of saliva connecting her lips to the tip of his shaft. With a soft yelp of surprise Sai was lifted up from behind, her thighs spread wide as Grillby's tip brushed against her slick entrance, "Beg." Grillby's breath was hot at her ear as he rubbed against her.

 

Gaster knelt between her thighs, one hand wrapped around Grillby's length, the other around his, pumping slowly as his long tongue taking a long lick against her folds, making her moan loudly. She leaned up against Grillby's warmth, arching her back as Gaster's tongue penetrated her. Sai moaned, Grillby's slick tip brushing against her, Gaster's tongue teasing them both with each pass making Grillby jerk his hips with a low groan. "Beg for me sweetheart...beg for my cock..." Grillby growled at her ear, a gasping moan escaping her lips as Gaster's sharp canine brushed against her clit. "Nnngh! Please! Please...I need...fuck me please..." She begged biting her lip as Gaster guided Grillby's cock to her hole, one sharp thrust making her cry out in pleasure. 

 

He was so hot inside of her and so...so much bigger than she'd had before. Grillby groaned as he filled her up, bottoming out against her cervix, a shiver running through her as she adjusted to him. Gaster's tongue licked and teased at her clit, Sai's legs shaking but unable to close due to Grillby's grip on them. "Good girl...so tight..." Grillby groaned as he started to move inside of her, slow at first but quickly picking up the pace, her arm moving up behind her the other instinctively going to the back of Gaster's skull as he sucked and licked at her.

 

"Nnnyeahhh! Fuck! Oh my god!!" She cried out in panting moans as Grillby pounded into her, Gaster growling against her clit, the feeling nearly overwhelming. "Such a...nnng...filthy mouth Sai...let's fix that..." Grillby growled, forcing her forward onto her hands and knees, sending her vision spinning for a moment before Gaster's shaft was shoved down her throat again. Grillby thrust into her from behind, Gaster thrusting into her throat, pinning her between them. Fuck! She'd never thought it would feel like this, being used like this...Sai moaned around Gaster's shaft, tongue running his length, swirling around the head with every pass. "That's our good girl...hnnngh..." Gaster groaned, Sai hearing them share a sloppy kiss above her as they thrust into her.

 

She could feel the coil in her gut tightening, her moans muffled by Gaster as her toes curled, back arched inward as Grillby hit deep inside of her. "You're close aren't...mmmnnnngg....aren't you baby girl? Hahhh...cum for me...cum on my cock..." Grillby's pace was relentless, driving her over the edge as she pulled away from Gaster, tongue lolling out of her mouth as she cried out in pleasure. "Sonof...so t-tight! Hngh!" Grillby growled, a wave of heat filling her up inside as he came. Grillby pulled out, juices running down the inside of her thighs as he breathed heavy.

 

"Go ahead and clean me off and give Gaster a chance to fill you up." Sai obeyed, turning around to face Grillby who leaned up against her headboard, his eyes watching her as she licked his hot shaft, Gaster positioning himself behind her, leaning over and kissing the space between her shoulders softly. One of his hands crept between her legs, finger tip rubbing at her swollen clit, making her keen as she glanced up at Grillby who groaned, bucking his hips. "Let's give him a show hmmm sweetheart?" Gaster purred at her ear, pressing his shaft between her folds, impaling her on him slowly.

 

"Now that's a pretty face..." Grillby wrapped his fingers around his cock, pumping it slowly in front of her face as Gaster began to move. Sai was still so sensitive, her moans loud and keening as Gaster moved within her slow and deliberate. His fingers pinched at her clit, kissing over her back as he rolled his hips into her. "Sai...such a good girl...such a sweet little tease you've been tonight..." Gaster breathed against her skin, kissing and sending pleasant chills down her spine. Grillby pumped his shaft, Sai taking initiative and swirling her tongue around his head, earning her a groan of pleasure from the flame elemental.

 

He was moving so slow...she wanted more...needed him to move faster as she pushed back onto Gaster. He chuckled at her ear and she knew that he was doing it on purpose. While Grillby seemed more direct in his approach, Gaster seemed to want to play with his meal as he stopped moving altogether, making her whine softly. "Awwww, do you want more precious?" Gaster asked, Grillby flicking his gaze up to the skeleton with a smirk. "Y-yes...please..." She panted, the seductive tone of his voice doing wonders to her body.

 

"Then you have to ask right." Gaster nipped at her shoulder, licking along her throat up to her ear. "Say, master please fuck me." He whispered into her ear, sending a chill down her spine, goosebumps rising on her skin. "We own you sweetheart. From now on..." Gaster slowly pulled back his hips, only the tip of his shaft remaining inside of her as he spoke into her ear, "We are your masters. And you belong to us. Now, ask me right." Sai's submissive nature was in hyperdrive as he commanded her. Grillby watching her reaction as she caved into her instincts. "Master...please, please fuck me...Make me yours...please master." She cried out as Gaster slammed into her, Grillby stifling the sound by thrusting into her mouth with a groan.

 

"Good girl..." Gaster groaned, thrusting deep and wild into her core, her moans muffled around Grillby's shaft. She was in absolute bliss, moving between them eagerly, taking them both at the same time. Wanting to please them. To please her Masters as they pleased her. She could feel her climax rising quickly once again, tightening around Gaster. "S-so close...Grillby?" Gaster asked the flame elemental who nodded, breathing heavily as he jerked his hips into her throat. She moaned around him desperately close to completion as they thrust wildly into her, chasing after their own orgasms. Sai's eyes went wide as her climax hit, harder than the first time, two low growls echoed in unison around her, Grillby grabbing her head and forcing her down on him, holding her there as string after string of heat hit the back of her throat, forcing her to swallow the strange tasting seed while Gaster filled her up inside, some of it leaking out of her.

 

They held her there as they rode out their highs, Sai shivering as she finished, using her tongue to clean Grillby slowly as he slowly let her go so she could breathe. "That's our good girl...Come here..." Gaster pulled out of her as she was pulled into Grillby's embrace, feeling full and satisfied. Grillby kissed her as Gaster moved to lay behind her, pulling the blankets over the three of them, his arms wrapping around her. "You did so good for us...did you like it?" Gaster asked as he curled around her. "Y-yes sir...I really did..." She was spent, nuzzling into the combined embrace of her masters, hearing them chuckle softly. "Good. Let's get some rest then...Good night Sai." Gaster kissed her lips, reaching up and pulling Grillby in for a kiss as well before settling in for the night. "Good night."


	6. Chapter 6

****

Sai nuzzled into the warmth, arms wrapped around her body and the soft sound of breathing soothing. Faintly she could hear the sound of a camera clicking and she frowned in her sleep. She didn't want to move but she could hear the clicking of the camera again and it was starting to irritate her. She just wanted to sleep...she'd earned it. Finally she couldn't stand it anymore and untangled herself slightly from the warmth of the embrace. With a groan she lifted herself up on her knees, brushing her long hair away from her face only to hear the sound of the camera again. Blinking, Sai turned towards the sound and saw Grillby standing there looking at the images on his camera with a smirk.

 

"Good morning." He greeted as she yawned. She was impossibly slow to wake even on good days, today was no exception as she tried to get her brain to form words. "Hey. What's with the pictures?" She asked, laying back down next to Gaster who was still asleep but had rolled over onto his back, Sai laying her head on his chest as he reflexively wrapped an arm around her back. So warm. Grillby took another picture, "I just thought you two looked all nice and comfortable and figured why not." Grillby put down the camera and came to sit behind her on the bed. "Come here."

 

She rolled over to face him, climbing into his lap and straddling his hips. "You remember what Gaster said last night right?" He asked, leaning up against her headboard, hands resting on her hips as she tried to recall what had been said in the heat of the moment. "You belong to us now. And us to you. This is just like any other relationship and cheating will not be tolerated. You have a problem then you come talk to us. Is that understood?" Sai nodded, sensing the serious tone in his voice. "Yes sir. I understand. I don't cheat, I never have in any of my relationships anyways." She responded, earning a smile from him as he kissed her.

 

"Good girl. Now I have something else I want to talk to you about. Your bed." Sai looked at him in confusion. "It's too small for all three of us. You and Gaster oh so lovingly dumped me on the floor this morning." Sai blushed in embarrassment, glancing over at Gaster who was still sleeping peacefully. "I'm sorry. I mean it's been just me for so long...I guess I didn't really think about it." She turned back to Grillby who was smirking at her.

 

"It's fine. We'll go out and get you a new one today since both of us are free today. So why don't you and I go and make some coffee hm?" He gave her a tap on her ass and she hopped off of him, following him into the kitchen and getting out the coffee while he put water into the maker. Sai yelped softly as Grillby picked her up and sat her on the counter, a shiver running down her spine as the cold of the counter hit her skin only to be warmed up as Grillby stepped between her parted legs, wrapping his arms around her and pulling her in for kiss.

 

She leaned into his kiss, god was he so warm. It made sense since he was literally made of flames but still, compared to other humans this was just...well it was amazing. "Good morning." Gaster's sleepy voice interrupted the two of them, making Sai jump slightly in surprise, Grillby chuckling as he turned to face the skeleton.

 

"Good morning." Sai greeted, watching as Gaster was drawn like a moth to a flame to the freshly brewed coffee, opening and closing various cabinets in search for a coffee mug. "Top left over the sink." She finally told him, a grumbled "Thank you" coming from him.

 

Gaster poured himself a cup of coffee, taking several sips before he sighed softly, turning around to face the two of them. "Better. Now, what are we talking about this morning?" Gaster asked as Grillby moved to make himself a cup, Sai following suit as she stood on her tip toes to give Gaster a quick kiss in greeting. "We're going bed shopping today." Grillby said as he stirred in some creamer, Gaster looking at him curiously.

 

"We just got a new bed. Why do we need to go out and get another one?" Sai blushed and looked up at Gaster. "Apparently you and I accidentally kicked Grillby out of my bed last night. So he says I need a new one so the three of us can sleep together comfortably." She explained and Gaster snickered, taking another sip of his coffee while Grillby rolled his eyes.

 

"We'll have to stop by the house before we head out so we can shower and get a change of clothes. We hadn't intended on staying the night last night." Gaster winked over at Sai who blushed and smiled up at him. "I could meet you there? I've got to do a couple things here anyways." She suggested, the two of them nodding in unison.

 

"We can do that. But first I'm going to finish the rest of this coffee before I even think of getting started with my day." Sai smiled and decided to let the two of them wake up while she went to get into the shower. As she washed up she ticked off the stuff that she had to do for the day, she was going to need to wash some clothes, the sheets from last night, she needed to vacuum and then she needed to make sure she paid some of her bills, do a commission. Just to name a few things. 

 

When she got back out of the shower they were already dressed and talking quietly together. "We'll send you a message when we're ready. Thank you for the coffee." Gaster leaned down, capturing her lips in a kiss, stepping aside for Grillby to do the same. "Okay, see you guys in a bit then." She waved them off as they closed the door behind them, her apartment feeling a little more empty now. She sighed as she looked around and saw the coffee mugs in the sink, going back to her room to get some clothes on.

 

She was about to go into the laundry room when there was a familiar tapping on the glass of her window, a large black lizard creature sitting on the sill patiently waiting for her. "Hey buddy, welcome back." She opened the window, letting the creature inside, hearing his familiar purring growl as he brushed against her hand in greeting. "You want to come keep me company while I do laundry Slink?" She asked and he hopped up onto her shoulders, careful to keep his claws from digging into her skin as she grabbed a pen and sketchbook along with her laundry stuff, going into the laundry room.

 

Sai sat on the counter, Slink curled up in her lap, sleeping soundly as she doodled him as a warm up. She was putting her clothes into the dryer when she got a text message from Grillby. He told her not to eat anything because they were going to take her out to lunch, with an added stipulation that she wasn't supposed to wear any underwear. She blushed and texted back as she finished off her laundry, Slink crawling into the warm clothes as she brought it back to her apartment.

 

She finished putting her laundry away, shot off a couple of emails and got dressed. "Alright, you gonna be good here by yourself buddy?" She scratched underneath Slink's chin as he gave a soft chirp in reply. "I'll be back later. Time to go shopping for a new bed with the guys." Slink yawned and curled up in a beam of sunlight for another nap as Sai left, hopping into her car and driving off towards the mall. It felt a little weird sitting in her car without underwear. She parked and headed into the large mall, going to the meeting place and adjusting her skirt as she sat on a bench.

 

The guys weren't there yet so she just leaned back and scrolled through her social media, answering questions and messages on her Tumblr account. It was such a nice day out considering it was winter so wearing a skirt wasn't totally out of the question. She was answering a question from one of her followers when she heard a low whistle of appreciation, jerking her back into the real world as Gaster and Grillby stood in front of her.

 

"Long time no see sweetheart. You ready to go?" Gaster smiled down at her, Sai standing up to greet them. "Yeah, I'm ready when you guys are." Gaster grabbed her hand as Grillby wrapped an arm around her waist, leaning down and kissing the top of her head. "Did you do what I told you to do?" He asked quietly as they walked in the crowd of people. A blush colored her cheeks as he discreetly slipped his thumb into the top of her skirt, his finger brushing against her skin.

 

"Good girl." He purred and she leaned into him, squeezing Gaster's hand slightly as they walked towards the mattress store. Just before walking in though Grillby had to take a phone call, staying outside so he could talk to whoever it was without interruption. "Hello! How can I help you today?" One of the salespeople came up to her and Gaster, their fingers interlinked as Gaster smiled politely at the salesperson.

 

"Yes. We're looking for a new bed. the larger the better." The salesperson grinned and Sai could tell he was excited about the possibility of a hefty commission as he brought them to the most expensive bed on the showroom floor and started rambling on about how it was the absolute best on the market and you could adjust the height and the softness with just a simple press of a button. Gaster let him go on with his spiel before moving on to a less expensive bed and sitting on it. "Sir, that model is outdated. This is a much better-" The salesperson started but Gaster waved him off.

 

"Scientifically this bed is just as effective as the one you're trying to sell. Thank you. Have a nice day. We will tell you when we are ready to purchase." Gaster smiled politely at them and they shuffled off, disappointed leaving Sai and Gaster to themselves. "What do you think of this one?" Gaster asked and she sat on the edge of the bed. It was a little too soft for her taste so the two of them went around looking for something that she liked. Grillby finished his phone call and soon joined them the three trying out different beds and talking among one another.

 

"Excuse me. I just wanted to say that I think it's wonderful that you two monsters adopted a human. It's so progressive of you." An older woman in her forties came up, tapping Gaster on the shoulder to get their attention, all three of them turning to face her.

 

Sai blushed and shrank into herself a little nervously. Grillby sat on the bed, sharing a glance with Gaster who turned back to the woman. "I mean I know some people may think that monsters are terrible parents or influences but seeing the three of you together, it just warms my heart. I for one am a big monster supporter. Are you guys looking for a bed for her dorm room? You look like you're about college age." The woman turned her smile on Sai who honestly didn't know how to respond.

 

"She is in college and we are buying her a new bed. Sweetheart, come sit on my lap. Daddy wants a kiss." Grillby smirked, patting his leg as Sai stared at him wide eyed and blushing a vibrant shade of red. "Go on. Don't keep leave him hanging." Gaster chuckled as Sai sat on Grillby's lap, one arm snaking around her waist, the other pulling her face to his in a deep kiss.

 

The woman gasped as they broke for air, Sai's face flushed as Gaster leaned over and kissed her just as passionately. "We're very progressive." Grillby chuckled as the woman quickly walked away muttering something under her breath as both monsters started laughing.

 

Sai relaxed a little bit, rubbing her thighs together, feeling a little aroused from the encounter. Maybe she had a new kink that she hadn't realized. There was that strange tingling feeling when Grillby had called himself Daddy..."Sai? Are you...are you turned on right now?" Grillby asked quietly while Gaster went to talk to the salesperson about purchasing.

 

"No. I'm just...okay yeah. A little bit." She blushed as Grillby leaned in and nuzzled the crook of her throat, kissing and nipping at her skin. "Hmmmm...you like sitting on daddy's lap, your bare ass sitting on my leg like a naughty girl?" He purred into her ear, sending a chill down her spine that pooled in her stomach.

 

"Hmmmm might not make it home to play with you...I think there's a unisex bathroom close by..." Grillby nipped at her earlobe, Sai's body trembling slightly. "The bed is going to be shipped to your house by tomorrow-and what exactly are you two doing?" Gaster asked, crossing his arms over his chest, brow bone raised as he smirked down at the two of them.

 

Grillby pat her ass for her to get off of him as he stood, Sai readjusting her skirt. "We need to use the restroom." He stated simply and Gaster chuckled, shaking his head as the three of them walked out of the store and headed to the nearest bathroom. "Be good you two, I'm going to go get some blankets and a few other things for the bed. Video." Grillby gave him a quick kiss, dragging Sai into the family bathroom and locked the door.

 

"On your knees baby girl." Sai knelt on the cold floor in front of him watching as he pulled down his zipper, exposing his erect member. After a moment he pulled out his phone and pointed it down at her. "Now suck daddy's cock baby." Sai blushed and opened her mouth, fingers wrapping around the base and swirling her tongue around the thick head, glancing up at Grillby who licked his lips. "No time for playing sweetheart, don't want to keep people waiting." Grillby grabbed the back of her head, fingers tangling in her hair as he thrust into her mouth, making her moan in surprise as he thrust his hips into her.

 

Sai's hands braced against his thighs as he held her head still, rocking his hips into her mouth. "Let me see those pretty eyes of yours sweetheart." Sai flicked her eyes up at him, receiving a soft groan of approval. "That's my girl...good girl." She moaned at the praise, the sound vibrating around his shaft as he pumped into her. She sucked and licked with each thrust, looking up at him and into the camera as he groaned. "Fuck babe..." He breathed, pulling her head back, her tongue lolling out of her mouth, saliva connecting them as she panted for breath.

 

"Go over to the counter, bend over and spread those legs for daddy like a good little girl." Sai licked her lips and did as she was told, facing the mirror she could see Grillby come up behind her and smack her ass cheek hard enough to make her yelp in surprise, seeing the smirk on his face reflected back to her. He grabbed one of her legs and placed it on the counter as he positioned himself at her entrance, rubbing the head of his cock at her entrance already slick with need.

 

"Look at how wet you are from sucking my cock." Grillby moved the camera to her entrance, rubbing against it enticingly making her moan softly as he pressed into her folds ever so slightly. "I want you to ask me to fuck you good. Nicely." Sai licked her lips, looking up at him in the reflection of the mirror with a needy expression. "Please...daddy...Please fuck me..." Sai keened as she rubbed against him eagerly. Grillby smirked at her as he teased her some more. "Since you asked so nicely..." Grillby thrust into her, a long moan echoing in the bathroom as Grillby slammed into her.

 

Sai bit her lip as she tried to keep from being too loud, the only sounds were the slapping slick sounds of Grillby pounded into her entrance, heavy breathing and Sai's strangled moans as she watched Grillby in the mirror, the sight oddly arousing. She gripped the counter as she felt her body tense, close to orgasm as Grillby continued to film her, cock pounding into her from behind. "You want me to...f-fuck hahh...to fill up that pussy baby?" He groaned as she thrust harder into her and she could feel herself right on the cusp.

 

"Nnnnngh! Oh gahh! P-please cum! Haaaahhnnnngg...fill me up daddy...Please." She begged as she arched her back, looking directly into his eyes in the mirror pleadingly. He cursed under his breath as his thrusts became more wild, jerking in and out of her relentlessly as she tried her best to contain the moans by covering her mouth with her hand, eyes locked on him the entire time as she came around him hard, tightening her walls on his thick cock which made him groan and throw his head back slightly. He pumped into her hard and fast, groaning as his hot seed spurted into her core, filling her up to the brim.

 

Grillby shuddered as he finished, pulling out and pointing the camera back at her pussy, spreading her lips as their juices ran down her leg while she tried to catch her breath. "Turn around and have a taste for me sweetheart." Sai did as she was told, taking her fingers and rubbing some of their juices onto them, using her tongue and licking them clean while Grillby watched.

 

"Mmmmm good girl. Do you want Gaster to fill your pussy next sweetheart?"He asked as he came over to kiss her neck, holding the phone out to capture both of them. "Yes. Yes I do. I want him to fill me up too, just like you did. You make me feel so good." Grillby chuckled and pulled her face to his for a kiss, "Hear that babe? She wants you to fill her up. Don't keep her waiting." Sai watched as he turned off the camera, kissing her again as he cleaned himself off, handing her a towel to do the same.

 

"You did so good. Let's go find Gaster and grab something to eat." Grillby pulled her in for another kiss, Sai leaning into him with a satisfied smile on her face.

 


End file.
